This research will focus on chemical characterization and the mechanism of action of heat-stable enterotoxins (ST) produced by porcine, bovine and human strains of enterotoxigenic (ENT ion) Escherichia coli. The mechanism of action of ST will be studied using the rat perfusion model to measure fluid and electrolyte fluxes and possible enzyme-mediated absorptive responses. Ion fluxes in isolated porcine intestinal epithelium will be observed. The binding of radioactive ST to intestinal cells in isolated loops and to purified intestinal membranes will be studied. The nature of the receptor site(s) for ST will be characterized and identified. Additional work will look at the immunogenic properties of ST conjugated to different carriers and development of a rapid diagnostic test. The subunit structure of purified heat-labile enterotoxin (LT) produced ENT ion E. coli will be characterized and the mechanism of action studied using whole cells and lysates of pigeon erythrocytes. The interaction of purified LT from porcin and human strains with small intestinal cells in isolated loops, purified intestinal membranes and pigeon erythrocyte membranes will be studied. Binding phenomena and the receptor(s) for LT will be characterized.